In recent years, demands for display apparatuses which can display three-dimensional images, namely, 3D images are rapidly increasing. Various studies about methods to display three-dimensional images have been conducted in past days, and still now, research and development about those are conducted briskly. As methods to display 3D images, which are currently considered notable, there have been proposed methods using binocular parallax.
Three-dimensional image display apparatuses using binocular parallax are roughly classified into two groups using the following methods. One is a method to create different images into left and right eyes by using special glasses (hereinafter, referred as “a method using glasses”). The other is a method to project different images for right and left eyes created by a three-dimensional image display apparatus at spatially separated regions without using special glasses (refereed as “a glasses-less method”).
The former “method using glasses” is a method suitable to the situation that plural observers view a relatively large screen at the same time and is used for movie theaters and televisions. The latter “glasses-less method” is a method suitable to the situation that a single observer views a relatively small screen. This method which allows observers to view three-dimensional images easily because observers are free from bother in wearing special glasses and is expected to be applied to various displays of mobile phones, digital still cameras, video cameras and notebook computers.
As an example of display apparatuses of the glasses-less method which can display three-dimensional images, Japanese Unexamined Patent Application Publication (JP-A) No. 2006-030512 discloses the following liquid crystal display apparatus. As shown in FIG. 21, there are arranged 3×3 pixels 6 in the X-axis and Y-axis directions in the disclosed liquid crystal display apparatus to form a matrix. One of the pixels 6 is composed of 6 sub-pixels RR, RL, GR, GL, BR and BL. In the liquid crystal display apparatus, one pixel composed of the six sub-pixels 61 emits two sets of light fluxes to be projected onto the left and right eyes of an observer, where each set of light fluxes is composed of three light fluxes in red (R), green (G) and blue (B) which construct a color image. Sub-pixel RR is a sub-pixel for displaying a red image for the right eye, and sub-pixel RL is a sub-pixel for displaying a red image for the left eye. Similarly, sub-pixels GR, GL, BR and BL are a sub-pixel for displaying a green image for the right eye, a sub-pixel for displaying a green image for the left eye, a sub-pixel for displaying a blue image for the right eye and a sub-pixel for creating a blue image for the left eye, respectively.
The liquid crystal display apparatus has a structure including liquid crystal panel 2 and lens-array sheet 3 put on the liquid crystal panel 2 (see FIG. 22 and FIG. 23). The liquid crystal panel 2 includes, as shown in FIG. 22, a matrix of pixels wherein sub-pixels RR, RL, GR, GL, BR and BL are arrayed in the X-axis direction at pitch of 2×Ppx and in the Y-axis direction. The lens-array sheet 3 includes cylindrical lenses 31 arrayed in the X-axis direction at pitch of Plx to form an array. As shown in FIG. 23, red light for the right eye emitted from sub-pixel RR is projected onto region ZR in the space through the cylindrical lenses and red light for the left eye emitted from sub-pixel RL is also projected onto region ZL in the space through the cylindrical lenses. When an observer comes to the position that right eye 9R of the observer is in region ZR and left eye 9L of the observer is in region ZL, the observer sees only an image for the right eye with right eye 9R and sees only an image for the left eye with left eye 9L, which allows the observer to perceive a three-dimensional image based on the images displayed by the liquid crystal display apparatus. Further, by displaying the same image on both of sub-pixels for the right eye and sub-pixels for the left eye, the liquid crystal display apparatus allows an observer to perceive a two-dimensional image. In view of the existing state that apparatuses for displaying images do not always display three-dimensional images and the frequency of displaying three-dimensional images is less than that of displaying two-dimensional images, it is important for display apparatuses to have a property to display two-dimensional images additionally to three-dimensional images for reasons of actual use.
However, the above-described liquid crystal display apparatus disclosed in JP-A No. 2006-030512 caused a problem that observers easily perceive moiré patterns when the liquid crystal display apparatus displays two-dimensional images thereon. Descriptions about a mechanism of generation of the moiré patterns will be given below. Cylindrical lenses do not have lens effect in the direction of the lens axis but have lens effect in the direction perpendicular to the lens axis. Under the condition shown in FIG. 22, the direction of the lens axis corresponds to the Y-axis direction and the direction perpendicular to the lens axis corresponds to the X-axis direction. When liquid crystal panel 2 is put at a position around the focal point of cylindrical lenses 31 of lens-array sheet 3, as shown in FIG. 23, light emitted from the liquid crystal panel 2 is projected through cylindrical lens 31 in the direction inclining at an angle against the Z axis, and the angle is defined depending on the relationship of the top of the cylindrical lens and the position of the light along the X axis on the liquid crystal panel 2. Therefore, when the intensity of light emitted from the liquid crystal panel 2 varies corresponding to its position on the X axis, the intensity of the emitted light varies corresponding to the light-emission angle. That is, under the condition that the liquid crystal panel 2 has light-shielding sections 80 which do not emit light and each light-shielding section 80 extends in the Y-axis direction, such the condition makes angular directions in which light does not exist among angular directions of light emitted from the liquid crystal panel 2, and those angular directions are perceived by an observer as black regions. That is the mechanism of generation of the moiré patterns. A liquid crystal display apparatus employing a parallax barrier in place of the cylindrical lenses also causes a similar condition.
Since each of the above-described light-shielding sections 80 is located between two neighboring sub-pixels arranged along the X-axis direction in the liquid crystal panel 2, each of the regions which looks black (regions Zd in FIG. 23) exists between an area where an image for the left eye is projected and an area where an image for the right eye is projected. Under the situation that the liquid crystal display apparatus displays a three-dimensional image, an observer moves his or her face to an appropriate position so as to adjust the left eye and the right eye to appropriate positions for perceiving an three-dimensional image based on displayed images. However, under the situation that the liquid crystal display apparatus displays a two-dimensional image, it is difficult for an observer to find the appropriate positions. Therefore, when the observer's face moves to a certain place, the eyes can be located in the regions which look black, which can deteriorate the display quality of the display apparatus significantly.
As a method to restrict the moiré patterns, there is known a method disclosed by JP-A No. H10-186294. FIG. 24 illustrates sub-pixels 61 of a liquid crystal display apparatus which can display three-dimensional images disclosed in JP-A No. H10-186294. As described above, when the intensity of light emitted from the liquid crystal panel varies corresponding to its position on the X-axis, it makes moiré patterns. The intensity of light emitted from a certain position on the X axis in the liquid crystal panel corresponds to the size ratio of an opening section and a light-shielding section in a slice obtained by cutting the opening sections of the liquid crystal display apparatus along the Y-axis direction at the certain position on the X axis. Therefore, the issue of the moiré patterns can be solved by keeping the size ratio of an opening section and a light-shielding section constant regardless of its position on the X-axis. Sub-pixels 61 disclosed by JP-A No. H10-186294 are arranged with light-shielding sections which extend along the Y axis with inclining at angle θ against the X axis. Assuming that the inclining light-shielding sections are “e” in width (see FIG. 24), width “d” of the size of the inclining light-shielding sections taken along the Y-axis direction can be expressed by the following expression (1).d=e/cos θ  (1)
The total size of opening sections, taken along the Y-axis direction, in an area including an inclining light-shielding section, is given by the total sum of sizes “b” and “c” shown in FIG. 24. As far as side “Et” and side “Eb” defining the form of the opening section are parallel with each other, when the total sum of the sizes is taken at any of positions ranging in the X-axis direction, the total sum of the sizes becomes constant regardless of the positions. On the other hand, in an area including no inclining light-shielding section, as far as side “Et′” and side “Eb” defining the form of the opening section are parallel with each other, size “a” of the opening section shown in FIG. 24 is constant regardless of the positions ranging in the X-axis direction and agrees with the total sum of sizes “b” and “c”, by adjusting size “f” to agree with size “d” (see FIG. 24). Herein, sides “E1”, “E1′” and “Er” are parallel with each other.
There are known any other methods to restrict moiré patterns other than the method disclosed by JP-A No. H10-186294 (for example, JP-A Nos. 2005-208567, 2008-092361 and 2012-215830).
However, it has been found that a problem of “a sense of horizontal stripes” can be caused when the pixel layout for restricting the moiré patterns disclosed in JP-A No. H10-186294 or others, is applied to the liquid crystal display apparatus which can display three-dimensional images disclosed in JP-A No. 2006-030512. That is, under the condition that a single color is displayed uniformly over the entire screen, observers feel that pixel rows neighboring in the Y-axis direction have different luminance and/or different colors from one another on the screen and perceive thin horizontal stripes on the screen, which is referred as “a sense of horizontal stripes” hereinafter. Such the sense of horizontal stripes is felt by observers strongly when the observers are going to observe details in a narrow area on a display apparatus, and such the phenomenon makes the display quality of the display apparatus deteriorate significantly. The present invention seeks to solve the problem.